Many industries, most notably the semiconductor, microelectronics, optoelectronics, microelectro-mechanical systems, nanotechnology, pharmaceutical, radio pharmaceutical, microlithography, and biotechnology industries, require large amounts of high-purity organic solvent fluids for various drying, cleaning, analytical, and manufacturing processes. For example, in the manufacture of modern integrated circuits, it is known that organic solvent fluids come into direct contact with the device materials. Such fluids include process and treatment chemicals, etchants, strippers and organic solutions containing polymers, esters, acids, and amines. Organic solvent fluids of various compositions are used to clean, develop, rinse, and dry wafers; prime surfaces; remove edge deposits; strip photo resist; and deposit dielectric materials. The lower purity forms of these organic solvent fluids may contain undesirably high amounts of particulate matter and various other impurities including water, trace metals, and other ions, all of which can negatively impact circuit performance. For example, the presence of excess chloride ions may cause corrosion to form on metal features of the circuit, resulting in circuit failure. Also, the presence of excess metal ions in some dielectric materials can negatively affect the voltage stability and drift in semiconductor devices.
The majority of commercially available organic solvent fluids used in the semiconductor industry have a high purity level, with a contamination level ranging from about 1 to about 100 parts per million (ppm). While this level of purity is acceptable for most industries, it is unacceptable for the above-identified industries, which require organic solvent fluids having trace metal element or ionic impurity levels of less than one part per billion (ppb). Because commercially available organic solvent fluids contain excess suspended particles, ionic impurities, and trace metals, they may be subjected to an additional purification procedure before use.
Various purification procedures for removing dissolved cationic and anionic impurities from organic fluids exist. One such purification procedure involves using ion-exchange materials to remove alkaline metal salts from an aqueous alkanolamine solution, as described in U.S. Pat. No. 4,795,565. Specifically, certain salts present in refinery gases and produced during the ethanolamine extraction of carbon dioxide and hydrogen sulphide are selectively removed. The spent ethanolamine solution, containing between about 50 weight percent and about 80 weight percent water, is passed over various stationary beds of strong anionic and cationic resins.
Another purification procedure involves using ion-exchange materials to remove alkaline metal salts from an alkanolamine solution used in industrial gas treatment systems, as described in U.S. Pat. No. 5,162,084.
Another purification procedure involves selectively extracting certain aromatic hydrocarbons present in a mixture of paraffins. As described in British Patent No. 2,088,850, an anionic ion-exchange media can be used to remove acidic and/or chloride corrosive impurities from aqueous 1-methyl-2-pyrrolidone (NMP). More specifically, aromatic hydrocarbons from a mixed hydrocarbon source can be removed by directing a recycled NMP-water stream through an ion-exchange media.
Another purification procedure, described in Russian Patent No. 2,032,655 of Magomedbekob et al., involves the deionization of aliphatic alcohol and diols using water-saturated stationary beds of anionic and cationic resins, thereby reducing the electrical conductivity of the organic solvents.
Another purification procedure, described in the Buragohain et al. article entitled “Novel Resin-Based Ultra Purification System for Reprocessing IPA in the Semi-conductor Industry,” involves using cation ion-exchange materials in combination with a molecular sieve and activated carbon materials to recycle an aqueous 2-propanol solution of semiconductor manufacturing waste.
Another purification procedure involves using a sulphonic ion-exchange media having acidic SO3H active groups to purify dimethyl sulphoxide, as discussed in U.S. Pat. No. 5,990,356.
Because there are various opportunities for the purified organic solvent fluid to be contaminated, a second concern is in-system contamination. For example, once the high purity organic solvent fluid is available for use, it is typically placed into an empty canister, drum, tanker, or other container, which may contain contaminants. These containers are subsequently transported to the device fabrication facility and placed into the existing chemical distribution system, where their contents may have a different purity level than the contents of the existing chemical distribution system. Thus, if the incoming containers of organic solvent fluid having one concentration of impurities are added to existing amounts of organic solvent fluids having a different concentration of impurities, the resultant chemical purity levels within the entire chemical distribution system and/or at the end-use point of connection may be adversely affected. Also, the organic solvent fluid may be contaminated as a result of use and exposure to contaminated equipment or to the articles of manufacture. Further, semiconductor wafers and flat panel displays are often processed using repeated immersion cycles in which the wafers or displays are dipped into and out of multiple baths for cleaning purposes, resulting in contamination of the liquid in the baths. As a result, the high purity organic solvent fluids may be further contaminated by the manufacturing equipment and the existing liquids therein.
Maintaining a consistent process chemical purity level is especially important in the semiconductor and electronics manufacturing industries, because any variation in impurity concentration can adversely impact the stability of the manufacturing system and significantly reduce the quality of the final product. Consequently, stringent quality-control procedures are typically utilized to maximize chemical consistency and minimize the impact of these purity fluctuations.
In an effort to maintain high purity organic solvent fluids within their point-of-use chemical systems, many manufacturers replace all of the organic solvent fluids contained therein. However, this process is very expensive because it necessitates replacing the expensive high purity organic solvent fluids and because the manufacturer has to dispose of the resultant hazardous waste. A method of increasing the purity of the organic solvent fluids within the chemical distribution system is to replace the particle filters. However, this is also very expensive because each of the pleated TEFLON™ filters, for example, costs between about $500 and about $5,000. Further, the replacement process may require shutting down the entire system.
Therefore, it is desirable to have available a cost-efficient method of and system for purifying organic solvent fluids that become contaminated during manufacture, use, shipment, or handling. The purification method preferably increases the purity of the organic solvent fluids such that the purified organic solvent fluids have trace metal element or ionic impurity levels of less than one ppb and more preferably of less than 0.1 ppb.
Further, it is desirable to have available a cost-efficient method of and system for increasing both the purity and the consistency of the commercially available organic solvent fluids within the purification system such that over time the amount of impurities found in the organic solvent fluids remains stable.